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(CNN)Texas Sen. Ted Cruz picked up six delegates in Colorado on Saturday, shutting out Donald Trump and Ohio Gov. John Kasich on the opening day of the state's complicated delegate selection process, the state GOP said.

Cruz supporters won all the delegate slots in the state's 1st and 6th congressional districts, representing the Denver and Aurora areas. Delegates from the state's five other districts will be selected on Thursday and Friday.

The state GOP opted not to hold a traditional presidential preference vote for 2016 and instead directly elects 21 delegates at a series of seven congressional district-level meetings, which began Saturday. An additional 13 delegates will be selected at the state convention next Saturday in Colorado Springs.

Cruz now has 466 delegates overall, compared to 739 for Trump. Kasich trails with 145. A candidate needs at least 1,237 delegate votes in order to secure the Republican presidential nomination outright before the Republican National Convention in July.

Saturday's results in Colorado are part of the Cruz campaign's aggressive behind-the-scenes delegate strategy, focusing on the finer details of state-by-state delegate selection rules. Earlier in the day, the Texas senator was in Fargo, North Dakota, addressing delegates to the state's GOP convention, which will elect 25 national convention delegates on Sunday.